Escherichia coli ("E. coli") O157:H7, first isolated in 1975 from a patient with grossly bloody diarrhea, is now recognized as an important foodborne pathogen (Ministry of Health and Welfare, Information on the Detection of Pathogenic Microorganisms, 1996; Meng et al., Trends Food Sci. Tech. 5:179-185, 1994; Padhye et al., J. Food Prot. 55:555-565, 1992; Riley et al., N. Engl. J. Med. 308:681-685, 1983). In adults, the illness is usually self-limited. However, the more serious hemolytic uremia syndrome ("HUS") affects some of the infected patients, especially children and the elderly. The mortality rate of HUS is 3 to 10%. Most outbreaks have been associated with consumption of undercooked ground beef or raw milk. Cattle has been identified as an important reservoir of E. coli O157:H7. Person-to-person transmission has also been identified in some day-care center and nursing home outbreaks (Centers for Disease Control and Prevention, Morbid. Mortal. Weekly Rep. 42:253-257, 1993; Lior, Dairy Food and Environ. Sanitation 14:378-382, 1994; Padhye et al., J. Food Prot. 55:555-565, 1992).
Several methods have been developed for rapid detection and identification of E. coli O157:H7. Most of these methods are immunoassays for detecting the E. coli O157 somatic antigen (Huang et al., J. Food Prot. 59:170-174, 1996; Meng et al., Sci. Tech. 5:179-185, 1994). Confirmation of a positive result by either biochemical or serological tests, such as Vero cell assay or a test for the presence of H7 antigen, are required.
DNA probes and polymerase chain reaction have also been used to detect E. coli O157:H7 (Meng et al., Sci. Tech. 5:179-185, 1994). Although DNA-based methods are sensitive, there are several major drawbacks. First, they detect the presence of nucleic acid of the target bacteria rather than the viable bacteria themselves. Second, most of the DNA-based methods are designed to detect the genes that encode verotoxin or virulence-associated marker of verotoxin-producing E. coli, and are not specific for E. coli O157:H7. In addition, DNA-based methods are cumbersome and expensive.
A coliphage named AR1 has been found to infect E. coli O157:H7 with high specificity (Ronner et al., Journal of Food Protection 54: 944-947, 1990).